High-frequency signal-receiving system



Aug. 11, 1925. 1,549,310

LE ROY E. HUMPHRIES HIGH FREQUENCY SIGNAL RECEIVING SYSTEM Filed Oct, 22. 1923 2 Sheets-Sheet 1 Attorney/s.

Aug. 11, 1925. 1,549,310

LE ROY E. HUMPHRIES HIGH FREQUENCY SIGNAL RECEIVING SYSTEM Filed Oct. 22. 1923 W: I m H a I run I 2 Sheets-Sheet 2 QR fll l l I I M M I I I 1 Patented Aug. ll, i925.

stares earner @Fllitihf.

LE ROY.E.,HUMPHBIES, O1 ATLANTA, GEORGIA, ASSIGNOR OF ONE-FOURTH TO ASA W'. CANDLER, F ATLANTA, GEORGIA.

HIGH-FREQUENCY SIGNAL-RECEIVING SYSTEM.

Application filed October 22, 1923. Serial No. 669,998.

To (5Z1 whom it may concern.

Be it known that L Li: ROY E. Hui-i- IHl-LI s, a citizen of the United States, residing; at Atlanta, in the county of Fulton and State of Georgia have invented certain new and useful improvements in Highfrequency Signal-Receiving Systems. of which the following is a specification.

My invention relates broadly to radio communication, and more particularly to a radio receiving systen'i used for the reception of high frequency current signals wherever such reception or signals are subject to interference from static or strays of anuntuued or aperiodic character that excite the receiving system by shock excitation or by induction, leaving it free to (is cillate at its own natural period or to interference offered by local transmitters in proximity of the receiving:' station.

L ne of the objects of this invention is to provide a system for the reception of signals wherein the detrimental or interfering effect of the static or stray currents is minimized or e in'ii ated, thus providing a more reliable and eiiicient iystem for the reception of the signals.

Another object of the invention is to pro vide a circuit arrangement for a receiving station for enabling simultaneous transmission and recc tion of signals. the transmit tor being located in close proximity to the receiving station but producing: no lni'81"f 11'- cure with the functioning: of the receiving; apparatus.

A further object of the invention is to provide a receiving: circuit arrangement having a pair of differently tuned energy colcuits conncctet lo differentially lecting err coupled circuits tuned to substantially the same frequency with a separate circuit cumulative coupled with the resultant field of the difiercntialiy coupled circuits and connected to independent radio receiving apparatus which by virtue of the differential .peration of the associated circuits will respond to a selected incoming frequency to t e exclusion of strays or undesired frequencies. I

Another object of the invention is to provide a receiving system particularly adapted for cr inuous ware reception wherein a pair of differently tuned receiving circuits are balanced one against the other and a local source of oscillations supplied to each circuit stood from the specification hereinafter following by reference to the accompanying drawings, in which Figure 1 illustrates one form of the invention employing a link circuit between the receivers with a local oscillator arranged to operate on each of the recci 'inga; circuits; and Fin. 2 shows aform of the invention in which each of the receivers operates with self-excited oscillations for heat re: ption with a final detection circuit 'ccted to each of the receiving circuits. is is understood however that I do not limit myself to the plf 'tltflilfll illustration or form rcn as l may adopt various forms of the circuits within the scope of my invention.

11 a broad sense the invention divides i:.cci.*in;1 circuit into two branches, granch lie. 1 and branch No. 2. It may be assumed that branch l-To. l is. tuned to frequency Y, the frequency of the desired signal. while branch No. 2 is tuned to a diffe ent frequency Y. Branch No. 1 will contain the signal c rrcnts and the static currents also. Branch Ho. 1 is excited or heterodyned by a locally genera-ted frequency equal to frequency Y, the incoming frequency of branch No. Branchllo. 2

excited or hcterodyned by a locally generated frequency equal to frequency X. the incoming frequency of branch No. 1. The resultant frequency in each branch is the same and has very closely the same wave form for damped waves.

The two branches are balanced against each other and the interfering; or static currents balanced out, leaving the signal currents unaffected. The manner in which this is done most c'iiciently will now be described with reference to the circuit diagram.

Referring to Figure 1, reference character 1. denotes an antenna. 3 primary inductance, i a variable condenser, and 5 a ground forming; one branch circuit. Simiiiirly. branch circuit No.2 is formed by quencies are substantially different, as will antenna 2, primary inductance 2 1, variable condenser 25, and ground 26. While I have shown the radio frequency energy collecting circuits as being formed by an antenna ground system, it will be understood that other forms of radio frequency energy col-, lecting circuits may be employed. A tuned circuit is connected to each of the branch circuits. Secondary inductance 6 is coupled with primary inductance 3 andtuned comprising secondary inductance 23 inductively coupled with primary inductance '24:, the secondary inductance 23 being tuned by variable condenser 22. An electron tube detector is connected with this secondary circuit, the detector including filament electrode 28, grid electrode 29, and plate electrode 30, with grid condenser and grid leak :27 in the grid circuit thereof.

The input circuits of the electron tubes are tuned to the'frequency of the respective radio frequencyenergy collecting circuits to which they are coupled, which frebe hereinafter described. The output circuits of each of the electron tubes comprise .plate battery 14-, inductance 16, and variable tuning condenser 15 in the circuit of the detector connected to branch No. 1, and plate battery 20, inductance 18, and variable tuning condenser 19 in the circuit of thedetector coupled to branch No. 2. The filament electrodes 12 and 28 of the tubes are heated from filament battery 13. A source of local oscillations is provided at the receiving station which may consist of an electron tube oscillator. The tube is represented as having filament electrode 52, grid electrode 5 1 and'plate electrode 51. The grid and plate circuits of the oscillator are interlinked by inductances and 55. The plate circuit contains high voltage battery 53. A link circuit is provided which is energized by the local oscillator through inductive coupling 48 and tuning condenser 49. A pair of branch circuits are connected with the link circuit at opposite extremities thereof and arranged to supply different frequencies to the input circuits of the separate electron tube detector circuits. The branch of the link circuit including inductance 4 1 and tuning condenser 45 is coupled with the input'circuit of the electron tube detector in branch No. 1 by means of a coil 9 in the secondary circuit. The branch of the the input circuit of the electron tube detector in branch No. 2 by means of inductance 21 in the secondary circuit.

Inductances 16 and 18in the output circuits of the separate electron tube detector filament electrode 33, grid electrode and plate electrode 34; connected for amplification of the energy picked up by inductance 17. The output circuit of this amplifier contains primary winding 35 of a' coupling transformer and plate battery 36. Secondary Winding 38 is inductively coupled to the primary winding 35 and arranged to deliver energy to a rectifier circuit. The rectifier circuit may be an electron tube having filament electrode 41 gridelectrode 40, and plate electrode 42 with a grid condenser and. grid leak 39 in the grid circuit thereof. The filament electrodes 33 and 41 may be heated by means of filament battery 37. The plate circuit of the rectifier tube is energized from high voltage battery 36 and a responsive device, such as telephone receivers 43, is connected therein.

In describing the operation of this inven tion I will assume that antenna 1 is tuned. to a frequency of 400 kilocycles, which is the frequency of the desired incoming signal. The corresponding secondary circuit 6 and 7 is also tuned to this frequency and the sig nal current is impressed on grid 10 and fila ment 12 in the manner shown. Antenna 2 is tuned to 300 'kilocycles, thus eliminating 1 the signal of antenna 1, which is an entirely different frequency. The corresponding secondary circuit 23'and 22 of antenna 2 is tunedto 300 kilocycles and will contain the interfering currents set up by shock excitation in antenna 2. These currents are impressed on grid 29 and filament 28 in the manner shown. Thus, antenna 1 con tains the signal as well as the stray currents. Antenna 2 contains the stray currents only. It is assumed for theimmediate purpose of discussion that the stray Waves are nondirectional and that a reasonable distance between the two antennae will not effect the phase values of the interfering currents set up in the two antennae. This will be discussed in more detail hereinafter.

The secondary circuit of antenna 1 to gether with the grid-filament circuit of the tube connected therewith, is coupled to the linkcircuit by coil 9 in the secondary circult and coil of the link circuit. Coil is tuned by condenser 45 so that their nat ural period is equal to 300 kilocycles, the frequency of antenna 2. The secondary circuit of antenna 2, together with the gridfilament circuit of the tube connected therewith, is coupled to the link circuit by coil 2t in the secondary circuit and. coil 46 in the link circuit. Coil 16 is tuned by condenser 47 so that their natural period is equal to l kilocycles, the frequency of antenna 1.

The link circuit coupled to the local oscillator in the manner shown, and coil 48 0f the link circuit should preferably be tuned to the frequency of the local os' cillator. Though not absolutely essential to operation but for best operation and greater stability, the frequency of the local oscillator should be the median frequency of the two antennae, in this case 350 kilocycles. The link circuit will, therefore, be excited by induction and forced oscillation into three. major frequencies. These fre quencies are 300, 350, and 400 kilocycles. Thus there will be impressed on the grid of the electron tube coupled to antenna 1a localfrequency of 300 'kilo'cycles, the frequency ofantenna 2. Any currents in antenna 1 will react with the local frequency of 800 kilocycles so that the plate circuit of the electron tube connected to antenna 1 will contain-an A. C; component,

the amplitude of which will rise and fall at the rate of 100 kilocycles per second.

The induc ance 16 in the plate circuit of thistube is tuned by condenser to a The inductance 18 in the plate circuit of this tube is tuned by condenser 19 to a frequency of 100 lrilocycles. It will readily be seen that with referenceto the static or stray currents the plate circuits of the two tubes contain the same resultant frequency and very nearly the same resultant wave form due to this frequency. Now coil 16 contains the signal currents as well as the static or stray currents. Coil 18 contains the static or stray currents only. Therefore, if the two coils are coupled to a third coil 17, in such a manner that their fields oppose each other with reference to coil 17, then the static currents are balanced out and the signal currents only will be impressed on coil 17, which. is tuned by condenser 31 to the frequency of 100 kilocycles. Coil 17 and condenser 31' are connected to another tube where the sig nal is either detected or further amplified, shown in the diagram. The frequenu'iven above are arbitrary frequencies for the purpose of illustration and it is rradily understood that the frequencies may be any value so long as the principle of operation disclosed herein is adhered to.

iig. shows another form of the invention, in which the autodyne method used in stead of an external or local oscillator. Means are introduced in the plate circuits of each receiver for securing a rcactive effect on the respective input circuits and the electron tubes produce their own beat frequencies. Inductance 56 and condenser 57 are adjusted so that the plate circuit is tuned to the frequency of antenna 1. Inductance 58 and condenser 59 are adjusted so that plate circuit 11 is tuned to the frequency of antenna 2. The remainder of the circuit operates as described in connection with Fig. 1, a detector being nterposed in the mutually coupled circuit for actuating the responsive device 43.

It will also be apparent that in the description given the median or mean fre quency of the two antennae, in this case 350 lrilocycles, will also produce the same resultant frequency in both branch circuit No. 1 and branch circuit No. 2, that is. the resultant would be in this case 50,000 cycles. "But this frequency does not effect coil-17 since it is tuned to 100,000 cycles.

Separate antennae are not entirely necessary; one antenna may be divided into two branches and balanced in the manner explained, in which case the two branches are fitted with liters or tuned impedances having very low decrements. The use of one antenna avoids the problem of phase values that often arises with'the use of separate antennae when the interfering s 31c or stray wave is of a directional character; The use of one antenna has the principal disadvantage that any tuning of one branch also affects the other branch,'mal ing the tuning and operation rather diflicult. This, however, is not a disadvantage in the case of a fined communication service between two transmittingstations, for in this case, once the adjustments are made they need not be changed unless the transmitter constants are changed, which is not intended.

It is desirable that the various couplings be made as loose a possible in order to prevent radiation of the oscillation frequencies. Vfhen using two or separate antennae, as shown in the diagram, the two antenna should be close together as possible with out causi any material interference because of the action of one upon the other.

If the two antennae are a considerable distance apart, the interfering currents are apt to be out of phase with reference to time in the two antennae and the voltage set up in one will not equal the voltage set up in the other. This is because the interfering wave will have different values of amplitude for one antenna than it Will'for the other. The voltage impressed on the secondary circuits of the two antennae can be controlled by proper coupling.

In connection with phase control, some improvement can be had. in this respect where conditions demand it by the use of phase control circuits in the plate circuits of the tubes connected to the two antennas. This, however, is not necessary under average conditions for practical control of the circuit, for with properly chosen constants in the system sufficient balance of the interfering currents is secured for all practical purposes. here only one antenna is used, all difficulty by reason of phase displacement is avoided.

In localities where static waves are propagated from some particular direction and it is desired to use two antennae, then the two antennae can be so placed that waves from that direction are in phase with reference to the two antennae. Itis, of course, understood that whatever types of antennae are used, they should have as nearly as possible the same physical and electrical charac teristics. The same applies to the electron tubes used in the system. In actual construction and operation the proper component parts of the system should be perfectly shielded to prevent interference between them because of electrostatic or electromagnetic induction.

My invention finds particular application where it is desired to establish simultaneous transmission and reception between two stations under conditions where it is not possible to erect the receiving station and the transmitting station at any great distance apart. In this invention the receiving antennae need onlyto be placed a moderate or short distance away from the-transmitting antenna and placed so that the two. receiving antennae are in proper phase relation to the waves from the transmitting antenna.

Referring back'to the explanation of the operation of this invention in reference to the circuitshown in the drawing and the frequencies assumed, it will be seen that if the local transmittingstation be tuned to have a frequency of 350 kilocycles, which is equal to the mean frequency of the two receiving antennae, then the local signals will be balanced out along with the strays or static currents. The distant station would transmit at 400 kilocycles instead of 350- placed a sutlicient distance away and tuned to 4-50 kilocycles anc 350 kilocycles respec' tively. Thus the static currents as well as the local transmitter currents would be balanced out of both receiving circuits.

Elsewhere I have stated that the resultant frequency in the plate circuits of the two balancing electron tubes would have very nearly the same wave form. If the interfering antenna currents were induced by continuous or undamped waves, the resultant plate current frequencies would have identically the same wave form. The interfering antenna current oscillations are generally of damped form and the amountof this damping is controlled by the receiving system constants. For damped oscillations,

the difference in the wave forms ofthe re sultant frequencies in the plate circuits of the two tubes will be less the nearer the fre quency of antenna 2 approaches the frequency of antenna 1, provided the decrements of the corresponding circuits are the same. The two wave forms can, of course, be varied to a certain extent by variation of coupling and resistance in the antennas and secondary circuits. If the two antennae frequencies are as close together as working conditions will permit, the unbalanced potential represented by the difference in the resultant wave forms will never approach the maximum value represented by amplitudes of the interfering oscillations. The practical result of-this is to effect at all times a balance of approximately so that an average of only 15% of the voltage of the interfering damped oscillations remains unbalanced to effect/the incoming signal.

Under certain conditions of service where very long waves are employed intransmission as in trans-oceanic'wirelesscommunication and land line carrier wave systems, the operation of this invention is simplified by the employment of small properly designed While I have described my invention in connection with radio reception, it will be understood that I may apply the principles of my invention to carrier wave line wire systems and that various modifications of the invention may be made, and that I intend no limitations upon the invention other than are imposed by the scope of the appended claims. 1

What I claim and desire to secure by Letters Patent of the United States is as follows:

1. A radio receiving system, comprising in combination a pair of electron tube circuits including input and output circuits, radio frequency energy collecting means connected to said input circuits, said in ut circuits being tuned to different radio requencies and said output circuits being tuned to substantially the same frequencies, a link circuit interconnecting said input circuits, said link circuit including a local oscillator and a pair of branch circuits inductively coupled one with each input circuit and arranged to deliver a frequency equal to the frequency of the opposite input circuit, said output circuits being diflerentially coupled and arranged to deliver a resultant lield to an independent radio receiving circuit.

2. A radio receiving system, comprising in combination a p ir of electron tube circuits each including an input and output circuit, radio frequency energy collecting means connected to said input circuits, said input circuits being tuned to dili'erent radio frequencies and said output circuits being tuned to substantially the same frequency, a local oscillator having a frequency which is substantially a median frequency between said input circuits, a link circuit connected with said local oscillator, separate branch circuits included in said link circuit inductively coupled each with one o1". said input circuits, the frequency of each of said branch circuits being substantially equal to the frequency of said opposite input circuit, means differentially coupling said output circuits, and means cumulatively coupling the resultant field of said aforementioned means with electron tube apparatus.

3. A radio receiving system, comprising in combination a pair of electron tube circuits each including an input and output circuit, radio frequency energy collecting-a means connected to said input circuits, said input circuits being tuned to dillerent radio frequencies and said output circuits being tuned to substantially the same frequency, a local oscillator having a frequency which is substantially a median frequency between said input circuits, a link circuit connected with said local oscillator, separate branch circuits included in said link circuit inductively coupled each with one of said input circuits, means in each of said branch circuits for developing oscillations of a frequency above and below the frequency of said local oscillator, means differentially coupling said output circuits, and means cumulatiyely coupling the resultant field Oi s id differential coupling means with electron tube apparatus.

LE ROY E. HUMPHRIES. 

